Ethanedithiol, HS-CH.sub.2 CH.sub.2 -SH, is an important mercaptan which has found various industrial uses, particularly as an intermediate in syntheses and as a vulcanization agent. It can be prepared by treating mercaptoethyl acetate with ammonium hydrosulfide at high temperatures and under pressure with hydrogen sulfide. See French Pat. No. 2,102,936. It can also be prepared from dibromethane by reaction with thiourea followed by potassium, hydroxide (Organic Synthesis, Coll., vol. IV, p. 401, (1963)). In addition, its synthesis is described in Belgian Patent No. 668,463 by the reaction of sodium trithiocarbonate with dichloroethane; however, under the conditions described, one obtains a mixture from which ethanedithiol is isolated with a yield of only 38%.
Older methods which permit the preparation of ethanedithiol from ethylene trithiocarbonate: ##STR1## are described in the literature (cf. E. E. Reid, Organic Chemistry of Bivalent Sulfur, vol. I, Chemical Publishing, New York, pp. 41-42 (1958)). They consist in treating the ethylene trithiocarbonate with a base, a high temperature, and often under pressure. The yields of these reactions are in general very low and their reproducibility is low. Significant amounts, sometimes predominating amounts, of by-products are produced:
dimercaptoethyl sulfide: HS-CH.sub.2 CH.sub.2 -S-CH.sub.2 CH.sub.2 -SH PA1 heavy oligomers and polymers of ethanedithiol.
T. Taguchi, et al., (Tetrahedron Letters, vol. 41, pp. 3631-3634, (1969)) have produced ethanedithiol by treating ethylene trithiocarbonate with ethanolamine at 80.degree.-120 .degree. C. In spite of its convenience, this method presents the drawback of producing a large amount of organic by-products which are difficult to recover. With regard to the methods involving the reduction of AlLiH.sub.4 (S. M. Igbal, et al., J. Chem. Soc., p. 1030 (1960)), their cost is prohibitive for industrial use.
The above references are hereby incorporated by reference.